The invention relates to a switch valve connectable on the inlet side to a levelling valve via a control line and also electrically activatable, which has the positions raise, lower, drive and stop and which possesses, on a housing, a supply connection for a compressed-air source, an outlet and at least one connection piece for connection to pneumatic-spring bellows, a slide and a hollow double-valve body being switchable in the housing into the four positions via two switch pistons and two solenoid valves preceding these, and an inlet valve, an outlet valve and a shutoff valve for the respective connection and isolation of the lines thereby being formed in the four positions. This switch valve is a valve which is used for the arbitrary raising and lowering of the vehicle body and which is employed in a system where there is also a levelling valve for automatically keeping the height of the chassis of the vehicle constant during driving and during loading and unloading operations. A switch valve of the type described in the introduction is known within a control system from German Patent Specification 3, 344, 022. The switch valve is of two-circuit design. The switch valve is preceded by an electrical switch, via which the arbitrary raising and lowering can be selected and which, furthermore, also has a drive position, in which the automatic keeping of the chassis height of a vehicle constant via levelling valves is selected on the switch valve. Via two switch pistons and two preceding solenoid valves, a single slide is arranged displaceably in the housing and at its free end has a spring-suspended moveable part.
Moreover, the housing accommodates, in the region of the housing end facing away from the solenoid valves, a double-valve body which is made hollow for deaeration purposes and on which the outlet is therefore provided. The return spaces of the switch pistons therefore have to be connected separately to the atmosphere. This two-circuit design of the switch valve results in a relatively large constructional length, since the particular control line from the levelling valve and the particular line leading to the bellows of the circuit are respectively arranged successively in duplicate on the slide. If this known switch valve is modified to become a single-circuit type, some of the constructional length is omitted. However, the free cross-sections for aeration during arbitrary raising and for deaeration during arbitrary lowering are of equal size irrespective of the single-circuit or two-circuit design. This is a disadvantage for the two-circuit design or signifies here aeration and deaeration times which last longer.
A similar switch valve is also known from German Patent Specification 3, 424, 670. This switch valve is also of two-circuit design, at all events where the drive position is concerned, each circuit being controlled via a separate levelling valve. Here too, the control lines brought up from the levelling valves are provided radially on the housing of the switch valve, that is to say radially relative to the axis of the slides and switch pistons. The supply connection for the compressed-air source is connected to, and the inlet valve arranged at, the housing end facing away from the switch pistons, that is to say in the region of the end face located there. A closed double-valved body is used here. For each circuit there is at least one slide, so that for the two-circuit version two or three slides are assigned to two common switch pistons. The slides are of different design. Even if such a two-circuit switch valve were reduced to a single-circuit version, at least two slides would have to be provided, since either the inlet valve and the outlet valve are implemented on separate slides or else an additional slide is provided for this. Even in such a possible single-circuit embodiment, the free cross-sections of the inlet valve and the outlet valve do not change in comparison with the two-circuit version, and therefore longer aeration and deaeration times can result in the two-circuit version.
In a disadvantageous way, the known switch valves in the single-circuit and the two-circuit version require differently designed individual parts, especially slides, in each case. This not only makes production more expensive, but also presupposes, for proper functioning and proper installation after maintenance or repair, that the differently designed slides should not be installed interchanged. The free passage cross-sections of the inlet valve and of the outlet valve each depend, of course, on the absolute constructional size of the switch valve and on the prevailing geometrical conditions. However, it seems to be a fundamental disadvantage that these cross-sections are of the same size in both the two-circuit version and the single-circuit version.